Disable one-click signin for all platforms except windows.
Disable one-click signin for all platforms except windows.

BUG=121677
TEST=Make sure one-click signin is working only on windows. See crbug.com/110050
for a description of the feature

Review URL: https://chromiumcodereview.appspot.com/9969102

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@130528 0039d316-1c4b-4281-b951-d872f2087c98

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